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1
Portal, Christophe. "Approaches to high throughput physical organic chemistry." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2434.
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Over the past ten years, the development of High Throughput (HT) synthetic chemistry techniques has allowed the rapid preparation of libraries of hundreds to thousands of compounds. These tools are now extensively used for drug and material discovery programmes. The subsequent development of analytical capabilities to carry out qualitative and quantitative assessment of the compounds generated by HT synthesis as well as their HT screening has led to a dramatic broadening of the scope of HT techniques, ranging from image based analysis techniques to mass spectrometry (MS). Based on the latter, a range of solid phase and solution phase analytical constructs was developed to enable the qualitative and quantitative assessment of mixtures of small compounds, using positive electrospray MS as the sole analytical tool. A version of the construct allowed HT reactivity profiling to be carried out on a range of ten carboxylic acids, ten aldehydes and ten isonitriles in the Ugi 4-component condensation reaction. The effect of various parameters such as the concentration of the monomers on the reactivity was investigated. The elaboration of a HT Hammett parameter assessment method was made possible by the development of an electrophilic version of the construct. The value of the Hammett value was afforded by means of combinatorial Hammett plots and values were successfully evaluated in a HT mode for around thirty anilines with substituents in the meta and para position of the aromatic ring. Finally, analytical constructs were used in an attempt to evaluate enzyme reaction kinetics via the labelling of peptides and small drug fragment with coded constructs, to afford affinity determinations between the enzyme (protease) and peptidic or fragment based substrates.
2
Wan, Nan Chi. "Physical organic chemistry of N-substituted N'-cyanoguanidines." Thesis, University of Surrey, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308493.
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Geremia, Kara L. "Computational Estimation of the pKa's of Purines and Related Compounds." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1449754930.
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4
Zysman-Colman, Eli. "The chemical and physical properties of polychalcogens." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84864.
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The optimized synthesis of acyclic dialkoxy disulfides and aromatic polysulfides is described and their physical properties probed. A theoretical survey of dialkoxy disulfides and thionosulfites was undertaken in order to determine the most efficacious method for accurately modeling these compounds. In particular, the origin of the high barrier to rotation in the dialkoxy disulfides was determined to be due to a generalized anomeric effect resulting from two lone pair donations of each sulfur atom into each of their respective sulfur-oxygen antibonding orbitals. The origin of the high rotational barrier was also verified experimentally, in particular with respect to solvent and substituent effects. Complimentary to this thermal process, the decomposition of dialkoxy disulfides was also investigated. It was determined that these compounds decompose under first order kinetics via an initial asymmetric S-O homolytic cleavage. Activation parameters for both of these processes were determined.Theoretical modeling on the relative ground state energies of dialkoxy disulfides is also described. It has been ascertained that the equilibrium position between the two isomers can be influenced by the ring size of the molecule; larger rings promote the dialkoxy disulfide isomer. These modeling studies were successfully corroborated experimentally. Of note is the synthesis of a new 8-membered ring dialkoxy disulfides as well as novel 7-membered ring thionosulfites. These compounds were also confirmed by single X-ray crystallography.
The kinetics of desulfurization of acyclic aromatic tri- and tetrasulfides is described. Tetrasulfides were found to transfer a sulfur atom to triphenylphosphine over ten times faster than their trisulfide analogues.
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Milton, D. M. P. "Applications of mass spectrometry in physical, organic and inorganic chemistry." Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638196.
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Proton transfer reactions to monosubstituted benzenes have been studied in the gas phase as a function of protonation exothermicity using tandem mass spectrometry. The results have been interpreted in terms of competitive ring and substituent protonation and intramolecular proton migration with the aid of molecular orbital calculations. It is shown that during the reaction of CHs+ with fluorobenzene at temperatures less than 330K, proton transfer occurs preferentially to the F atom even though its proton affinity is approximately 180kJmol-1 less than the ring. Samples of ruthenium dioxide hydrate have been studied using the technique of mass spectral thermal analysis, before and after thermal activation. Two types of chemically bound water are identified, of which the loss of one is associated with the thermal activation. Headspace analysis of isotopically enriched gases evolved during reactions of these two forms indicates that the decomposition products contain oxygen atoms originating from the solvent. A glow discharge ion source has been constructed to fit an MS9 mass spectrometer. This source has been demonstrated to compare well with previous configurations for the analysis of metals in pin form. Fundamental studies show that the majority of the sputtering flux is observed to possess low energies, due to de-energising symmetrical charge transfer reactions in the cathode dark space. Ions of the cathode material possess higher energies, and it appears that sputtering of the cathode is mainly caused by atoms of the cathode material itself. Analysis of solutions has been performed using the flow discharge ion source. Lead and platinum were monitored at the ppb level in the urine of patients receiving cancer chemotherapy with the drug cis-platin. The data obtained support the idea that normally stored body lead is displaced by the platinum complexed in the drug, but only to a small extent. A novel investigation was made into the suitability of the technique for the analysis of organic species deposited on the cathode. The spectra of a wide variety of compounds are very similar to desorption chemical ionisation spectra. Although some sputtering does occur, the principal desorption process appears to be caused by rapid localised heating at the cathode surface.
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Korell, Ulrich. "Electrochemistry at organic conducting salt electrodes." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61171.
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Yach, Kimberly. "Miscibility and organization of organic monolayers : a solid-state NMR approach." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33044.
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The chemisorption, organization and dynamics of fatty acid self-assembled monolayers (SAMs) were investigated. Three types of fatty acid SAMs were studied: (i) alkane phosphonates, (ii) alkanoic acids and (iii) hydroxy carboxylates. The samples were produced by adsorbing the surfactants on the metal oxides and were characterized primarily by solid-state NMR techniques.Mixed monolayers were produced by co-adsorbing two different types of fatty acids, one of which was perdeuterated. The degree of miscibility was assessed by 1H-2H cross-polarization magic-angle-spinning (CP/MAS) experiments. Whereas phase separation in bulk fatty acid mixtures could be qualitatively detected, chain end intercalation in the case of mixed monolayers on colloidal substrates made determination of miscibility inconclusive.
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Wei, Ling 1961. "Structure and reactivity of monolayer and micelle interfaces." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56973.
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The research in this thesis is focused on the structure and reactivity of monolayer and micelle interfaces.The kinetic results of ring formations of a series of $ sigma$-($ omega$-bromoalkoxy)phenoxides in a cationic micellar environment (CTAB) revealed that the ring closure rate constants from the 7-membered ring to the 14-membered ring decrease by $ sim$6-fold. This is much smaller than that observed for a homogeneous reaction environment ($ sim$1500-fold). In addition, micellar effective molarities (EM)$ sb{ rm m}$ for these reactions are found to be 7 to 1900 fold greater than in homogeneous solution. This catatysis can be reasoned to originate from an increase in the ground-state free energy of the substrate induced by localization of the phenolate oxygen and alkyl bromide moieties at the polar micelle interface.
Monolayer isotherm studies establish a dependence of isotherm features on the structure of the phospholipid. It is found that the liftoff area increases as the position of the second hydrophilic group is located further from the dominate polar group. The transition pressure reaches its highest value when the substituent is in the 7-position. The condensed area for almost all these substrates gives nearly the same value ($ sim$45 A$ sp2$/molecule). These may be explained by that the molecules lie flatly on the air/water interface at high surface concentration after which the hydrophobic parts in a molecule are forced out of the water surface. The hydrophilic groups remain on the water surphase so as to produce a loop conformation. At high pressure all the molecules are approximately perpendicular to the water surface so as to form a highly dense packing state. The unusually broad first order phase transition in isotherms of some boloform and macrocyclic phospholipids is consistent with these substrates being reorientated at large areas to yield stable bilayers, trilayers, etc.
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Destiné, Jean-Nicolas. "Photodegradation of milled wood lignin." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69666.
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The photodegradation of lignin has been investigated using milled wood lignin (MWL) as a model. Solutions of MWL were exposed to ultraviolet (UV) light under aerobic and anaerobic conditions. Changes in the molecular weight distribution (MWD) of the lignin were assessed by gel permeation chromatography (GPC). To elucidate the chemical changes induced in the lignin by irradiation, infrared (IR) and UV spectra of the irradiated solutions were also studied. Irradiation under nitrogen causes the formation of both high molecular weight (MW) condensation products and low MW fragments; whereas, irradiation under oxygen yields only low MW fragments, similar to those found under nitrogen. Since the formation of condensation products can be attributed to free radical coupling, it follows that oxygen is probably reacting with free radicals to form peroxyl free radicals thereby avoiding condensation to higher MW products. Finally, the chemical basis of the photoinduced changes in the MWD of the lignin are discussed.
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Warner, Stephanie D. "High-pressure vibrational spectroscopic studies : (i) group 14 tetraphenyl compounds: (ii) hydrogen-bonded species." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0005/MQ44313.pdf.
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Razavi, Hossein. "Amino acid Schiff base methodology for the synthesis of glycosidase inhibitors: Polyhydroxylated pyrrolidines and indolizidines." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284049.
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The concise enantioselective syntheses of iminolyxitol and iminoribitol glycosidase inhibitors starting from benzophenone imines, of D-serine and L-alanine esters are presented. The reductive alkenylation of the Schiff bases followed by substrate-directed dihydroxylation and cyclization under various amino dehydration conditions (Ph₃P, CCl₄, or TEMPO oxidation/NaCNBH₃ reduction) gave the polyhydroxylated pyrrolidines in excellent overall yields (23% for 1 → 8a, 12% for 1 → 8b, 13% for 11 → 18a). In addition, synthesis of indolizidine glycosidase inhibitor 8- epi-swainsonine has been achieved. This approach featured trihydroxylated pyrrolidine 8a as an advanced intermediate in the synthesis of polyhydroxylated indolizidine alkaloid 25a, and highlighted efficiency in protecting group manipulation and stereocontrol in allylation with various allyltin reagents. In particular, a tandem protection-deprotection method converted pyrrolidine 8a to its corresponding partially protected analog which upon Swern oxidation and highly diastereoselective allylation afforded the required 3-carbon homologue. Subsequent hydroboration and cyclization furnished the polyhydroxylated indolizidine alkaloid in a limited number of steps and a good overall yield (29% for 8a → 25a). In a parallel sequence of reactions, pyrrolidine 8b was converted to 1,2-di-epi-swainsonine triacetate 25b in 32% overall yield.
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Snyder, Jamie Lynn. "A Symmetry Exploration into Covalent Tetracene Dimers with Tunable Electronic Coupling for Singlet Fission." Thesis, University of Colorado at Boulder, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3743722.
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One process that has the potential of efficiently harvesting solar energy is singlet fission (SF), a process by which one photon of light can produce two excited states. Investigations of three different series of bistetracene (BT) were used to explore the effect of symmetry on the rate and driving force of SF, as well as the electronic coupling. A dimer and the corresponding monomer were used to build a synthetic infrastructure and explore preliminary photophysics. All of the dimers were connected by one to three norbornyl bridges and exhibit various amounts of electronic coupling.
The first section of this dissertation will discuss a series of cofacial BT dimers with C2v symmetry that have one (BT1) to three (BT3) norbornyl bridges linking the two tetracene chromophores. Density functional theory calculations of BT1-BT3 were used to explore the SF driving force and the change in through-space versus through-bond contributions to the electronic coupling. The C2v symmetry was found to be unprofitable to SF, but vibrations accessible to the ground state would break the C2v symmetry. The thorough synthetic investigation of the monomeric tetracene-norbornyl bridge was developed to build a synthetic library that aided the synthesis of BT1, the first rigid SF dimer. Preliminary photophysics of BT1 and its monomer will also be described.
In the second portion of this work, the SF driving force, electronic coupling will be calculated for the second and third series of BT dimers, which are symmetry adaptations of BT1-BT3. In the second series, the orbital overlap of the norbornyl bridge and tetracene arms will be exploited by changing how the bridge and arms are connected to make dimers of C2 and Cs symmetry. In the final series, a heteroatom substitution of BT1 creates a series of C2 and Cs dimers that can be built using the synthetic infrastructure developed above. Both symmetry adapted series of BT dimers were found to lead to an increase in electronic coupling, which is expected to be productive for SF.
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Razzaghi, Mortezaali. "Quantum Tunneling in Hydride Transfer Reactions in Solution." Thesis, Southern Illinois University at Edwardsville, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1549836.
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The secondary kinetic isotope effects for the hydride transfer reactions from aliphatic alcohols to four carbocations (NAD+ models) in acetonitrile were determined. The results suggest that the hydride transfer takes place by tunneling and that the rehybridizations of both donor and acceptor carbons lag behind the H-tunneling. This is quite contrary to the observations in alcohol dehydrogenases where the importance of enzyme motions in catalysis is manifested.
14
Chen, Gang. "Experiments and modeling of the Belousov-Zhabotinsky reaction with 1,4-cyclohexanedione and ferroin." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/282877.
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We describe some observations during the induction period (IP) of a Belousov-Zhabotinsky (BZ) system with 1,4-cyclohexanedione (CHD) and ferroin in batch reactor. There are three stages during the whole course of the reaction: transitional period, the IP, and the post-IP. Two bifurcations are observed in this unique system: It starts with monostability (orange reduced steady-state) during the transitional period, switches to bistability (both blue oxidized and orange reduced steady-states) during the IP, and then eventually bifurcates to monostability (orange reduced steady-state) during the end of the IP. The stable orange steady-state is always excitable during the whole course of the reaction. The stable blue steady-state is not excitable during the blue IP: pulses cannot propagate and pacemakers cannot survive during this interval. As the medium ages, waves decrease their propagation speed except for the reduction step that speeds up during the end of the IP. We also investigate the change of ferroin and ferriin concentrations and photosensitivity during the IP. We find no analog to the situation suggested in the bromate-MA-ruthenium system, in that the oxidized state is experimentally excluded as the photosensitive species in this bromate-CHD-ferroin system. We construct here an Oregonator-like model that interprets the unique reduction step propagation before the second bifurcation. Based on the FKN mechanism with, we consider three reverse reactions, a breakdown of skeletal process C in the FKN model into three reactions with the addition of the hydrolysis of BrCHD. The model thus constructed endows bistability in some region of its parameter plane. We give a tentative interpretation of the differentiated speed between the reduction step propagation and that of the pulses, but rigorous mathematical mechanism awaits further investigation.
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Ogura, Hiroshi. "Probing the interactions between sterically demanding ferrihemes and histidine analogues. I. 2-D NMR studies of nonplanar ferriheme/bis(N-/2-methylimidazole) complexes; II. Synthesis of a trans-disubstituted tetraarylporphyrin with a bulky group near each potential axial ligation site." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284178.
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In a hemoprotein, histidine and other aromatic amines that ligate to the heme may encounter steric interactions from the following: (1) the peptide chains that form the pocket; or (2) the porphyrin ring that may have been distorted by the protein matrix or a distal ligand. Models that mimic these steric interactions need to be synthesized and studied in detail. The results of two research projects---both dealing with porphyrins that interact sterically with the axially ligated aromatic amines--are presented in this dissertation. In the first part, variable-temperature 2-D NMR studies of nonplanar ferriheme complexes are presented. Hemes are surprisingly flexible, and a significantly distorted conformation is accessible by the forces exerted by surrounding proteins and ligands. Iron(III) octaethyltetraphenylporphyrin ([Fe(III)OETPP]⁺) is a saddled macrocycle that could serve as a model for distorted hemes. Two low-spin [Fe(III)OETPP]⁺ complexes, one with two N-methylimidazole (N-MeIm) molecules as the axial ligands and the other with two 2-methylimidazole (2-MeImH), have been made, and their NMR spectra recorded as a function of temperature. Spectral assignment for the bis(N-MeIm) complex has been made through 2-D techniques. The NOESY spectra indicate that at about -40°C, the ring inversion halts while the axial ligand dissociation remains prevalent. The spectra of the bis(2-MeImH) complex at -85°C indicate that the dominant internal dynamics consists of ring inversion and a concerted rotation of the axial ligands. In the second part, the synthesis of a porphyrin with two sterically large groups near the potential sites of axial ligation is presented. In a bis(aromatic amine)/iron(III) complex of the alphabeta-atropisomer of 5,15-di-p-tolyl-10,20-bis[2,3-[(((hydrotris(3,5-dimethylpyrazolyl)borato)oxomolybdenio)dioxy]phenyl]porphyrin (1), the axial ligands are expected to be rotationally fixed. The synthesis of 1 is described. The corresponding trans -ditolylbis(dimethoxyphenyl)porphyrin (2) was synthesized from p-tolualdehyde and 2,3- dimethoxyphenyldipyrromethane in acidified aqueous sodium dodecyl sulfate in 16-25% yield. The demethylation of 2 and the subsequent reaction with HB(3,5-Me₂Pyz)₃(OCH₂CH₂O) afforded 1, characterized with FAB-MS (cation detection mode). The product most likely consists entirely of the alphabeta-atropisomer because of the steric constraint during the formation.
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Watson, Charles Todd 1967. "The effect of axial ligands and porphyrin substituents on the electronic ground state of low-spin iron(III) porphyrinates." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290636.
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To aid in the understanding of the electronic states of low-spin, bis-pyridine and -imidazole model complexes of the cytochromes b variable temperature proton NMR spectroscopy and EPR spectroscopy have been employed on a series of complexes of tetramesitylporphinatoiron(III), tetra(2,6-dibromophenyl)porphinatoiron(III) perchlorate, tetra(2,6-dichlorophenyl)porphinatoiron(III) perchlorate, tetra(2,6-difluorophenyl)porphin-atoiron(III) perchlorate, and tetra(2,6-dimethoxyphenyl)-porphinatoiron(III) perchlorate where the axial ligands were 4-dimethylaminopyridine, 3,4-dimethylpyridine, 3,5-dimethylpyridine, 4-methylpyridine, 3-methylpyridine, methylpyridine, 3-chloropyridine, 3-cyanopyridine, 4-cyanopyridine, N-methylimidazole, and 2-methylimidazole. Both paramagnetic iron(III) and diamagnetic cobalt(III) porphyrinates were synthesized. The 25°C proton NMR spectra of the cobalt(III) complexes were used to estimate the diamagnetic shifts of the corresponding iron(III) complexes. The proton NMR spectra of the iron(III) complexes were recorded from -90°C to +40°C. Small isotropic shifts and anti-Curie behavior in the pyrrole-proton resonances of the lower basicity pyridine complexes of tetramesitylporphinatoiron(III)+ indicate a (dxz,dyz)⁴(dxy)¹ ground state, and axial ∼4K EPR spectra of the lower basicity complexes and large gmax or rhombic EPR spectra of the higher basicity pyridine complexes of all of the iron(III) porphyrinates studied indicate a shift in electronic ground state from (dxz,dyz)⁴(dxy)¹ for the lower basicity pyridine complexes to (dxy)²(dxz,dyz)³ for the higher basicity pyridine complexes in all cases. The dipolar and contact contributions to the isotropic shift were determined based on estimates of the ground-excited state crossover point and geometric factors obtained from crystal structure data. Variable temperature NOESY and COSY spectra were successful in distinguishing meta from para resonances in the NMR spectra of the tetra-(2,6-dichlorophenyl)porphinatoiron(III) perchlorate bis-2-methylimidazole complex. X-ray crystallographic studies indicated parallel orientation of the axial ligands in tetra-(2,6-difluorophenyl)porphinatoiron(III) perchlorate bis-3,5-dimethylpyridine.
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Jiang, Xuan. "Self-assembly and spin-delocalization of copper clusters built on amidinate ligands and symmetry-reinforced cooperativity in tris(N-salicylideneamine)s for conformational switching and chemical sensing." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3344578.
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Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2008.Title from home page (viewed Oct 7, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 1017. Adviser: Dongwhan Lee. Includes supplementary digital materials.
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Robertson, Craig Collumbine. "Building complex systems based on simple molecular architectures." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2573.
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Over the past twenty years molecules capable of templating their own synthesis, so called self–replicating molecules have gained prominence in the literature. We show herein that mixing the reagents for replicating molecules can produce a network of self–replicators which coexist and that the networks can be instructed by the addition of preformed template upon initiation of the reaction. Whilst self–replicating molecules offer the simplest form of replication, nature has evolved to utilise not minimal self–replication but reciprocal replication where one strand templates the formation of not an identical copy of itself but a reciprocal strand. Efforts thus far at producing a synthetic reciprocal replicating system are discussed and an alternative strategy to address the problems encountered is proposed and successfully implemented. The kinetic behaviour of a self–replicating reaction bears two distinctive time periods. Upon initiation, the reaction proceeds slowly as no template exists to catalyse the reaction. Upon production of the template, the reaction proceeds more rapidly via template direction. During this slow reaction period, the system is prone to mistakes as the reaction is slow and unselective. The creation of an [A•B] binary complex through non–covalent recognition of reagents allows for the reaction to proceed at an accelerated rate upon initiation however products of such a reaction are usually catalytically inert and do not promote further template directed reaction. A strategy to combine the desired behaviour of an [A•B] binary complex with the further template directed autocatalytic self–replicating reaction is described and implemented. Supramolecular polymers consist of repeating monomers which are held together by non–covalent interactions. The strong association of a self–replicating template dimer is comparable to that of supramolecular polymers reported thus far in the literature which are produced by cumbersome standard linear synthetic procedures. Herein the application of self–replication to the field of supramolecular polymer synthesis is discussed. As the autocatalytic reaction to produce the template monomers occurs under the same conditions as required to allow polymerisation to proceed, the polymer is able to spontaneously form in situ by self–replicating supramolecular polymerisation.
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Stein, Natalia. "Spectroscopic and electrochemical studies of Shewanella oneidensis cytochrome c nitrite reductase, and improving c-heme expression systems." Thesis, The University of Wisconsin - Milwaukee, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3685085.
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In this work the redox properties of cytochrome c nitrite reductase (CcNiR), a decaheme homodimer that was isolated from S. oneidensis, were determined in the presence and absence of the strong-field ligands cyanide and nitrite. Four hemes per CcNiR protomer are hexa-coordinate with tightly bound axial histidines, while the fifth (active site) has one tightly bound lysine and a distal site that can be open, or contain exogenous ligands such as the substrate nitrite. Controlled potential electrolysis in combination with UV/visible absorption (UV-vis) and electron paramagnetic resonance (EPR) spectroscopies allowed for assignment of all heme midpoint potentials under each set of conditions. The studies show that the active-site heme is the first to be reduced under all conditions. The midpoint redox potential of that heme shifts approximately 70mV to the positive upon binding a strong field ligand such as nitrite or cyanide. When controlled potential electrolysis was carried out in the presence of nitrite, a concerted two electron reduction was observed by UV-vis, and a {Fe(NO)}7 reduced product was revealed in EPR. In addition, an asymmetry in ligand binding between active sites was revealed. This information is relevant for the interpretation of planned and ongoing mechanistic studies of CcNiR.
Over-expression, partial purification and characterization of another S. oneidensis multiheme enzyme, known as octaheme tetrathionate reductase (OTR), is also described herein. Though of unknown cellular function, OTR was previously reported to have tetrathionate reductase activity, in addition to nitrite and hydroxylamine reductase activities. The new results indicate that the expression of OTR has no effect on tetrathionate or nitrite reductase activities in the whole cell lysate, and only hydroxylamine reductase activity was substantially elevated in the overexpressing bacteria. OTR was stable in buffered solutions, but substantial activity loss during all attempts at column chromatography was a major obstacle to the complete purification. OTR also proved quite hydrophobic, so possible membrane association should be considered in future attempts to purify this protein.
Finally, this dissertation also reports attempts to improve S. oneidensis' ability to express foreign proteins. Though ideally suited to expressing c-hemes, it proved difficult to express carboxy his-tagged proteins in S. oneidensis because of persistent tag degradation. Attempts to knock out lon protease, a cytoplasmic carboxypeptidase, as well as the result of redirecting ccNiR from the SecA to the possibly more protected signal particle recognition (SRP) secretion pathway, are described.
Iron heme cofactors are single-electron transport moieties that play a crucial role in respiration. While oxygen is the electron acceptor of choice in aerobic atmospheres, microorganisms that live in anaerobic environments utilize other molecules with similarly high reduction potentials. S. oneidensis can utilize numerous terminal electron acceptors, including nitrite, dimethylsulfoxide and even uranium, thanks to a particularly rich array of multi c-heme respiratory proteins. Understanding of how the midpoint potentials and heme arrangements within the proteins influence these exotic respiratory processes is of interest in the fields of bioremediation and fuel development.
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Moore, Charles H. M. "Coordination chemistry of guanidine derivatives." Thesis, University of Nottingham, 1987. http://eprints.nottingham.ac.uk/14354/.
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This thesis describes an investigation of the coordination chemistry of l-cyanoguanidine (cnge), l-carbamoylguanidine (clge) and l-amidino-O-ethylurea (aOeu). Various copper(II) complexes of these analogous molecules were synthesised and characterised using mainly X-ray crystallographic and spectroscopic (infrared and UV-visible) techniques. Only bis (cnge) complexes were observed for copper(II) ions. The monodentate cnge ligands coordinated the copper(II) via their nitrile nitrogen atoms which were located in trans equatorial positions of the copper(II) ions's tetragonally distorted octahedral coordination sphere. Comparison of the infrared spectra of the complexes with that of cnge indicated that the spectra were highly diagnostic of coordination to the copper(II) ion. Clge exhibited amphoteric properties; the neutral, anionic and cationic derivatives formed complexes with the copper(II) ion. Whereas the former pair gave bis chelate complexes, the latter derivatives acted merely as a cation and was remote from the copper(II) ion's coordination sphere. Complexation of the neutral molecule resulted in a proton transfer from a terminal amine group to a central nitrogen atom permitting chelation via an imine nitrogen atom and a carbonyl oxygen atom to give a square planar CUN2O2 chromophore. The structural ramifications of this tautomeric shift were near identical to those observed upon cation formation which occurred by protonation of the central nitrogen atom of the uncoordinated neutral molecule. Unequivocal structural data could not be obtained for the complex of the anionic derivative. Spectroscopic analysis indicated, however, that chelation occurred via two imine nitrogen atoms to give a square planar CuN4 chromophore. Ethanolysis of cnge was effected in the presence of copper(II) ions and ethanol producing complexes of aOeu with a metal:ligand ratio of 1:1 or 1:2. In both complexes the ligand(s) chelated the copper(II) ion via two imine nitrogen atoms. The former complex, a dimer, exhibited a square pyramidal CUN2X3 chromophore (X=Cl,Br) whilst the latter complex was a bis chelate with a square planar CUN4 chromophore. Monitoring the Uv-visible and infrared spectra of ethanol solutions containing copper(II) chloride and cnge, indicated the presence of a plethora of reactions. However, it was concluded that initially mono and/or bis(cnge)copper(II) complexes, of low stability, were present in equilibrium with the reactants. Subsequently, ethanolysis of coordinated cnge occurred producing mono(aOeu)copper(II) complexes. Series first order kinetics approximated to those of the ethanolysis reaction. The ethanolysis process was then repeated to give the final product a bis(cnge)copper(II) complex.
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White, James Charles Peter. "Electrochemistry and organic chemistry of Cr(III) (EDTA)/Cr(II) (EDTA) and related couples." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315085.
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Sirbu, Elena. "Surface chemistry of cellulose nanocrystals." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33308/.
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Chemical surface modification of cellulose nanocrystals has had a fast development and increased interest from the scientific community as cellulose is the most abundantly available renewable polymer with many advantages such as nanoscale dimensions, high specific strength and modulus, high surface area, unique optical properties and the extraordinary modification potential to increase the application field. This thesis is aimed at expanding and improving upon the current knowledge in order to unlock new applications. Four esterification techniques were applied to the formation of cellulose nanocrystal esters of acrylic acid and methacrylic acid. The degree of surface substitution reached two to three surface hydroxyl groups (the maximum number) available for functionalization and this degree of substitution is very much dependent on the chosen esterification methodology. Two new fluorescently modified cellulose esters based on carbazole-9-yl-acetic acid and coumarin-3-carboxylic acid were synthesised using p-toluenesulfonyl chloride/pyridine and carbodiimide esterifications methods. Absorption and fluorescent properties were also measured and showed fluorescence proportional to the extent of surface functionalization. The maximum theoretically attainable degree of substitution could be reached while still maintaining the crystal structure of cellulose. Cationic cellulose nanocrystals were produced with a high positive surface charge when compared with the literature. The synthesis procedure was attempted in two steps and in a single step. The degree of modification for pyridinium acetate cellulose and methyl imidazolium acetate cellulose was found to depend significantly on the selected pathway. The cationic nature of the modifications was verified using zeta potential measurements and through adsorption of an anion dye. Synthesised cellulose acrylates and methacrylates were used in Thiol-Ene click reactions in which very mild and environmentally friendly reaction conditions proved to work from 10 min reaction times. Four different thiols were added, with and without hexylamine catalyst. In addition, an amidine functionalised cellulose nanocrystal was synthesised based on previously click-modified cellulose in a 2-hour reaction. Furthermore, the switchable behaviour of the synthesised nanoparticles was demonstrated by reverse bubbling with CO2 and Ar.
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Leaym, Xiaoxuan. "Synthesis and applications of novel resorcin[4]arene cavitands." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/745.
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Ren, Lei Birge Robert R. "Structure and excitation energy in retinals and retinal proteins." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2004. http://wwwlib.umi.com/cr/syr/main.
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Gundersen, Jennifer Lisa. "Acid dissociation of chloroguaiacols and pH dependent sorption to estuarine sediments." W&M ScholarWorks, 1995. https://scholarworks.wm.edu/etd/1539616676.
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Chloroguaiacols are common components of bleached kraft pulp mill effluent known to bioaccumulate in aquatic organisms, and sorb onto particulate material and sediments. Ionization properties of the chloroguaiacols must be known in order to explain their sorptive behavior in aquatic systems. to obtain this information, thermodynamic acid dissociation constants (p&K\sb{lcub}\rm a{rcub})& of guaiacol (o-methoxyphenol) and nine chloroguaiacols have been determined by spectrophotometric methods. These experimental p&K\sb{lcub}\rm a{rcub}& values have been compared with literature values, values predicted by the Hammett equation and predictions by quantum chemical calculations using MOPAC 6.0 with AM1 and MNDO Hamiltonian operators. Experimental and predicted acidities were linearly related, and the correlation and regression equations obtained have been used to calculate p&K\sb{lcub}\rm a{rcub}& values for those chloroguaiacols that were unavailable for experimental measurement. Sorption of chloroguaiacols onto sediments may result in reduced bioavailabilty to aquatic species, increased degradation rates or rapid burial. Conversely, it may result in increased exposure to deposit feeding species with subsequent transfer to higher trophic levels. The sorption of four chloroguaiacols (5-chloroguaiacol, 4,6-dichloroguaiacol, 4,5,6-trichloroguaiacol and tetrachloroguaiacol) with p&K\sb{lcub}\rm a{rcub}& values ranging from 9.06 to 6.06 was investigated on four estuarine sediments. The effect on sorption of aqueous phase pH, sediment organic carbon content and degree humification was investigated. Sorption coefficients, &K\sb{lcub}\rm d{rcub}&, were determined at two pH values (6.6 and 7.8). Linear relationships were observed between &K\sb{lcub}\rm d{rcub}& and both % total organic carbon(TOC) and % humic acids at each pH. &K\sb{lcub}\rm oc{rcub}& and &K\sb{lcub}humic{rcub},& sorption coefficients normalized to % TOC and % humic acids, were calculated. In addition to the amount of TOC present, the type of organic matter (ie. humic acids) is an important factor in sorption. Aqueous phase pH governs the ionization of chloroguaiacols. Sorption of the ionized and molecular species are different due, in part, to the different solubilities of the species and was reflected in the different &K\sb{lcub}\rm d{rcub}& values determined at each pH.
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Baddeley, Christopher Peter. "Structure-Function Studies of Modular Aromatics That Form Molecular Organogels." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243445872.
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Forsythe, Robert. "The Development of New Methods for Coal Sulfer Forms & Sulfur in Ash Determination." TopSCHOLAR®, 1993. https://digitalcommons.wku.edu/theses/2352.
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The development of new procedures to determine the amount and/or types of sulfur in coal and coal products is an ongoing process for coal scientists This development is driven by the problems and inconveniences of the current ASTM methods In this thesis, the work done at Western Kentucky University in the development of two new sulfur determination procedures will be described. The first procedure can be used as an alternative method for coal sulfur forms analysis with results comparable to the ASTM method. This procedure involves heating the coal samples at 365°C and 440°C for thirty minutes to selectively remove sulfur forms from the coal. The difference in the amount of sulfur remaining in the residues is the amount of pyritic sulfur in the coal This value, along with the ASTM D 2492 sulfate sulfur value can be used to calculate the amount of organic sulfur present in the coal. The second procedure described is an alternative method for measuring the amount of sulfur in coal ash. This method involves standardizing a Leco SC-432 sulfur analyzer using iron(II) ammonium sulfate and a modified weight method. The ash sample is then mixed with a carbon promoter and the total sulfur present in the ash determined. The problems encountered in the development of these two procedures and the advantages of these methods compared to the current ASTM procedures will be discussed.
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Kaushik, Vivek. "Synthesis of cyclen based receptors and their use in separations biotechnology." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2611.
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A number of purification techniques such as adsorption, centrifugation, chromatography, extraction, distillation, filtration, precipitation etc. to name a few, are commonly used for the purification. However, due to a constant need of purification of even more complex crude mixtures, be it reaction mixtures, various proteins and DNA from cell extracts or medicinal compounds and fragrances from plant extracts, scientists needed to consistently develop new and improved techniques of purification. One such great advancement in the field of chromatography was the development of affinity chromatography. It revolutionized the field of bioseparations technology, and the dream of single stage purification of complex biological substrates such as proteins, enzymes, co-enzymes, DNA, RNA etc. was realized. Development of various precipitation techniques involving phase tags, acid-base induced precipitation, host-guest interactions, chemoselective precipitation etc. further simplified purification procedures for few substrates. However, only a few examples of chemoselective precipitation are known in literature.1, 2 In 2005, our group synthesized a cyclen-based receptor.9 This receptor showed very strong and very specific affinity for the pyrene based dyes (HPTS, APTS, PTA) under physiological conditions, similar to that of the natural receptors for their ligands. Upon interaction with the dye, this artificial receptor formed a low solubility complex which had micromolar stability. Various structure and activity studies established the essentiality of the macrocyclic structure of the receptor for the dye recognition. We further decided to study the effect of various substituents on the aromatic ring on the binding and quenching affinity of the receptor. A series of receptors bearing electron-withdrawing and electron-donating substituents were synthesized (receptor 4-6). We also synthesized a receptor having aliphatic groups instead of aromatic groups attached to the thiourea group (receptor 7) as well as a receptor lacking thiourea linkage (receptor 8). The results of fluorometric titrations of these receptors were consistent with the previous structure and activity studies, as the receptors having electron withdrawing nitro- and bromo substituents (receptor 4 and 6 respectively) on the aromatic groups (have increased π-stacking) were better receptor than cyclen 1. Interestingly, the receptor 5, bearing an electron-donating methoxy groups on the aromatic ring, has also shown an increase in the affinity towards HPTS. We speculated that this increased affinity could be due to the higher affinity of receptor 5 towards Na+ which was essential for the proper arrangement of the receptor binding arms. The receptor with the aliphatic chain (receptor 7) showed a complicated complexation process and showed variable fluorescence quenching at various receptor concentrations. This behaviour was probably due to the formation of complexes of a various stochiometries. Expectedly, the receptor lacking thiourea group (receptor 8) did not show any interaction.Since this receptor-dye pair formed a low solubility complex of micromolar stability upon interaction, we hypothesized that this receptor-dye pair can be used in the selective separation of substrates by chemoselective precipitation. We reasoned that if the substrate of interest can be attached to the dye, this dye-substrate conjugate then can be selectively precipitated from the reaction mixture upon addition of the receptor. We tried our concept for the separation of lactose from lactose/sucrose mixture. Being a reducing sugar, lactose was labeled with APTS dye, whereas sucrose that lacks the reducing end, remained unmodified. Application of the cyclen receptor to this mixture resulted in precipitation of APTS-lactose conjugate, leaving sucrose as the only component in the solution.10 By coupling APTS dye with lactose via an imine bond, we were able to successfully isolate unmodified lactose from the conjugate by subsequent hydrolysis of the conjugate. Next, we decided to use this dye-receptor pair in affinity chromatography. We hypothesized that if the receptor can be immobilized on some solid support then it can be specifically used as an affinity support for the substrates which are attached to the pyrene-based dyes. A new receptor with a functional group on the cyclen core was needed to immobilize the receptor on the solid support. The receptor 11 having an aromatic primary amine group was synthesized. This receptor was successfully immobilized on the NHS activated agarose resin. A series of fluorometric experiments were performed to determine the specificity and binding ability of the affinity support towards the pyrene dyes. Initial results of these experiments indicated that the affinity support was very effective as indicated by almost 95% fluorescence quench of a solution of 50 nM HPTS and affinity resin. This work has opened several new venues of research, and the applicability of this dye-receptor pair in the fields of biochemistry, pharmacology, cell biology etc. will be explored.
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Reis, Adriana Karla Cardoso Amorim. "Estudo das Interações Eletrônicas das α-dietoxifosforilacetofenonas-para-substituídas e dos aspectos mecanísticos e sintéticos da obtenção dos dietoxifosforilésteres dos enóis das acetofenonas-para-substituídas." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/46/46135/tde-25082014-145144/.
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A primeira parte deste trabalho relata o estudo conformacional e das interações eletrônicas das α-dietoxifosforilacetofenonas-para-substituídas Y-Φ-C(O)CH2P(O)(OEt)2 (I), sendo Y= MeO, Me, H, Cl, Br, CN e NO2. Este estudo foi realizado através das espectroscopias no infravermelho, Ressonância Magnética Nuclear de 13C e 31P, apoiados por cálculos ab-initio 6-31G**. A existência de uma única banda simétrica da carbonila, tanto na transição fundamental como no 1° harmônico, conjuntamente com a constatação da ocorrência de uma única conformação de baixa energia através dos cálculos ab-initio, sugerem fortemente a existência na série estudada de um único confôrmero gauche. Os deslocamentos de frequência da carbonila do confôrmero gauche da série (I) mostraram-se negativos e aumentam significativamente em valor absoluto indo-se em para de grupos doadores a aceptores de elétrons. Contrariamente, a frequência de estiramento do grupo fosforila vPO diminui progressivamente no mesmo sentido. Este comportamento foi atribuído à ocorrência simultânea no confôrmero gauche da série (I) tanto da interação eletrostática como da transferência de carga entre o oxigênio do grupo fosforila (carregado negativamente) e o carbono carbonílico (carregado positivamente). Os estudos de Ressonância Magnética Nuclear de 13C mostraram uma constância nos deslocamentos químicos do carbono carbonílico na série (I), bem como uma expressiva blindagem do carbono carbonílico desses compostos em relação às acetofenonas correspondentes de referência. Já os deslocamentos químicos de 31P mostraram-se praticamente constantes ao longo da série estudada. Os dados de Ressonância Magnética Nuclear de 13C foram interpretados como sendo devido à ação simultânea tanto do efeito I do grupo dietoxifosforila como da transferência de carga do oxigênio do grupo fosforila ao carbono carbonílico que se encontram na relação espacial γ gauche. Os espectros no ultravioleta dos compostos da série (I) apresentam uma quase invariabilidade da energia da transição no → π* CO em relação às acetofenonas de referência correspondentes, com exceção dos compostos contendo em para substituintes fortemente atraentes de elétrons, onde ocorre uma discreta hipsocromia da transição no → π* CO. Este comportamento foi interpretado como sendo decorrente tanto da interação hiperconjugativa entre os orbitais π* CO e σ* C-P como também da interação de transferência de carga nO(PO) → π* CO, que é mais pronunciada quando o grupo fenacila dos compostos (I) contém grupos fortemente atraente de elétrons na posição para. A segunda parte da presente Dissertação relata o estudo das reações das α-halogenoacetofenonas-para-substituídas Y-Φ-C(O)CH2Hal com trietilfosfito em benzeno anidro à temperatura de refluxo de benzeno. Nessas condições observou-se a formação das α-dietoxifosforilacetofenonas-para-substituídas Y-Φ-C(O)CH2P(O)(OEt)2 (I) e dos enolfosfatos correspondentes CH2=C[Φ-Y][P(O)(OEt)2] (II), havendo mudança na proporção dos isômeros obtidos à medida que se varia tanto o substituinte na posição para do anel benzênico como a natureza do halogênio na posição α. O substituintes doadores de elétrons levam a formação preferencial dos cetofosfonatos (reação de Michael-Arbuzov) enquanto que substituintes aceptores de elétrons levam a formação preferencial de enolfosfatos (produto da reação de Perkow). Estes dados sugerem que a adição nucleofílica à carbonila com a formação dos enolfosfatos depende da afinidade eletrônica do orbital π* CO que estabiliza em maior ou menor extensão o estado de transição (III) que é o provável passo determinante da reação de Perkow. Assim sendo, no caso do para-nitro derivado que contém o LUMO (principalmente π* CO) de mais baixa energia ocorre a formação preferencial de enolfosfato, enquanto que o para-metoxi derivado onde o LUMO é desestabilizado ocorre formação preferencial do cetofosfonato. As proporções isoméricas de cetofosfonato e enolfosfato obtidos encontram-se linearmente correlacionadas com o σP de Hammet. O presente estudo evidenciou o efeito da natureza do grupo de partida (halogênio α à carbonila) na formação de enolfosfatos e cetofosfonatos nas reações estudadas, i.e constatou-se que quanto melhor for o grupo de partida para um mesmo substituinte na posição i>para das α-haloacetofenonas, maior é a proporção de enolfosfato formado em detrimento do cetofosfonato. O conjunto de dados acima descritos está de pleno acordo com a proposta mecanística de que o estado de transição (III) é o passo determinante da formação dos enolfosfatos na reação de α-haloacetofenonas-para-substituídas com trietilfosfito e praticamente exclui a possibilidade de outras propostas mecanísticas descritas na literatura.The first part of this work reports the conformational and electronic interaction studies of some α-diethoxyphosphoryl-para-substituted acetophenones Y-Φ-C(O)CH2P(O)(OEt)2 (I), where Y= MeO, Me, H, Cl, Br, CN and NO2. This study was performed by means of infrared, 13C and 31P Nuclear Magnetic Resonance spectroscopies supported by 6-31G** ab-initio computations. The single symmetrical IR carbonyl band observed both in the fundamental and in the first overtone regions along with the existence of a unique low energy conformation obtained by ab-initio calculations, strongly suggest that a single gauche conformer should be present in the whole series (I). The carbonyl frequency shifts for the gauche rotamers of the title compounds are negative and their absolute values increase progressively on going in para position from electron-donating to electron-accepting substituents. Contrarily, the phosphoryl stretching frequencies (vPO) decrease progressively in the same direction. These trends have been ascribed to the simultaneous occurrence of the attractive electrostatic and charge transfer interactions, which take place between the negatively charged phosphoryl oxygen and the positively charged carbonyl carbon atoms in the gauche rotamer of the title compounds. The 13C NMR data showed that the carbonyl carbono chemical shifts are practically constant along the whole series (I) and that these values are significantly upfield shifted with respect to those of the corresponding parent acetophenones. This behavior has been attributed to the simultaneous occurrence of the I effect of the α-diethoxyphosphoryl group along with the charge transfer which occur between the P=O and the C=O groups which are in the γ-gauche geometry. Furthemore, the 31P chemical shifts are almost constant along the series (I). The ultraviolet spectra of the α-diethoxyphosphorylacetophenones (I) present almost the same π* CO transition energies with respect to the same transition in the corresponding acetophenones, excepting the case of the title compounds which bear at the para position strong electron-attracting groups (nitro and cyano) for which a discrete hypsochromic effect of the π* CO transition has been observed. This behavior was ascribed on the grounds of the simultaneous occurrence of the hyperconjugative interaction (IIa) and their corresponding mono- (IIb) and di- (IIc) oxygenated derivatives Y-PhC(O)CH[SOnMe][P(O)(OEt2)] [II, n=0 (a), n=1 (b)] and n=2 (c)]; c) α-bromo, α- ethylsulfonyl-para-substituted acetophenones Y-PhC(O)[Br][SO2Et] III. This study was performed by means of Infrared, Nuclear Magnetic Resonance, Ultraviolet spectroscopies, ab initio computations and X-ray diffraction analysis. For the α-ethylsulfinylacetophenones (Ia) the cis conformer predominates over the gauche one while in the case of the α-ethylsulfonylacetophenones (Ib) the gauche conformer is the more stable relative to the quasi-cis one. The α-methylthio-α-diethoxyphosphoryl acetophenones (IIa) present only a single stable conformer which bears the (SMe) group in a syn-clinal (gauche) geometry and the [P(O)(OEt2)] group in the quasi-periplanar (quasi-cis) geometry with respect to the carbonyl group. The α-methylsulfinyl-α-diethoxyphosphoryl acetophenones (IIb) display two stable conformations corresponding each one to a different diastereomer. The most stable conformer CSSS presents the methylsulfinyl group [MeS(O)] in a quasi-periplanar (quasi-cis) geometry and the diethoxyphosphoryl group [P(O)(OEt2)] in a anti-clinal (gauche) geometry relative to the carbonyl group. The second less stable conformer corresponds to the CRSS diastereomer and displays both the [MeS(O)] and the [P(O)(OEt2)] groups in a syn-clinal (gauche) geometry. The α-methylsulfonyl-α-diethoxyphosphoryl acetophenones (IIc) presents only a single stable conformer bearing both the [MeSO2] and [P(O)(OEt)2] groups in a sin-clinal geometry with respect to the carbonyl group. The α-bromo-α-ethylsulfonylacetophenones III present a single stable conformation bearing the the [SO2Et] group in a syn-periplanar (quasi-cis) geometry and the [Br] atom in a syn-clinal (gauche) geometry relative to the carbonyl group.
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Chubb, Andrew Michael. "Organogermanium Chemistry Germacyclobutanes and digermane Additions to Acetylenes." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/822062-dbCcAk/native/.
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Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2036" Andrew Michael Chubb. 12/12/2003. Report is also available in paper and microfiche from NTIS.
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Forbes, Safiyyah. "Hydrogen-bond driven supramolecular chemistry for modulating physical properties of pharmaceutical compounds." Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/3756.
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Olivares-Amaya, Roberto. "Quantum Chemistry in Nanoscale Environments: Insights on Surface-Enhanced Raman Scattering and Organic Photovoltaics." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10184.
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The understanding of molecular effects in nanoscale environments is becoming increasingly relevant for various emerging fields. These include spectroscopy for molecular identification as well as in finding molecules for energy harvesting. Theoretical quantum chemistry has been increasingly useful to address these phenomena to yield an understanding of these effects. In the first part of this dissertation, we study the chemical effect of surface-enhanced Raman scattering (SERS). We use quantum chemistry simulations to study the metal-molecule interactions present in these systems. We find that the excitations that provide a chemical enhancement contain a mixed contribution from the metal and the molecule. Moreover, using atomistic studies we propose an additional source of enhancement, where a transition metal dopant surface could provide an additional enhancement. We also develop methods to study the electrostatic effects of molecules in metallic environments. We study the importance of image-charge effects, as well as field-bias to molecules interacting with perfect conductors. The atomistic modeling and the electrostatic approximation enable us to study the effects of the metal interacting with the molecule in a complementary fashion, which provides a better understanding of the complex effects present in SERS. In the second part of this dissertation, we present the Harvard Clean Energy project, a high-throughput approach for a large-scale computational screening and design of organic photovoltaic materials. We create molecular libraries to search for candidates structures and use quantum chemistry, machine learning and cheminformatics methods to characterize these systems and find structure-property relations. The scale of this study requires an equally large computational resource. We rely on distributed volunteer computing to obtain these properties. In the third part of this dissertation we present our work related to the acceleration of electronic structure methods using graphics processing units. This hardware represents a change of paradigm with respect to the typical CPU device architectures. We accelerate the resolution-of-the-identity Moller-Plesset second-order perturbation theory algorithm using graphics cards. We also provide detailed tools to address memory and single-precision issues that these cards often present.
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Glynn, Daniel Joseph. "New aspects in aluminium promoted organic synthesis." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12048/.
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In the first chapter of this thesis the aluminium promoted zinc Schlenk equilibrium of FG-ArZnX/AlMe3 is shown to provide good access for the synthesis of chiral secondary alcohols. This practical asymmetric 1,2-addition to aliphatic and aromatic aldehydes uses only commercially available reagents and ligands. Enantioselectivity is provided by the use of (1R,2S)-dibutylnorephedrine (1,2-amino alcohol ligand) giving selectivity, in most cases, between 80-96% ee. Yields are moderate to good, typically alcohols are prepared in 50-97% yield. Uniquely the FG-ArZnBr species can be prepared in situ directly from Ar-Br or Ar-I, via the cobalt catalysed zinc insertion. Optimisation of the zinc insertion allowed for rate acceleration and a subsequent slight reduction in enantiocontrol. Furthermore, enantioselectivity of the reaction can be enhanced via the simple addition of LiBr to the FG-ArZnBr species. A LiBr promoter can dramatically enhance the enantioselectivity of such ‘home made’ reagents (from 30 to ca. 90% ee in one case), however studies to explain this effect have not been investigated. Further investigation into zinc source optimisation via electron microscopy and energy dispersive X-ray (EDX) spectroscopy, has highlighted the necessity to use small particulate zinc in the range of 2-10 muM and having little surface oxide. Stereo correlations of the secondary alcohol products highlight a reverse in stereochemistry compared to the ‘classic Noyori’ transition state for the addition of ZnEt2 to PhCHO using chiral 1,2-aminoalcohol ligands. Analysis and investigation of our system showed there was no non-linear effect associated with the process, suggesting the catalyst to be monomeric in solution. A second thesis chapter describes facile DABAL-Me3 mediated preparation of aromatic and aliphatic amides. This procedure allows the coupling of a wide range of functionalised primary and secondary amines and esters, secondary amines and allows formation of versatile Weinreb amides. Microwave irradiation provides an improved rate of reaction allowing excellent yields (51-99%) in short reaction times (8-16 min). Wide applicability is shown in the variation and tolerance of a wide range of functional groups in both coupling partners. Functional groups tolerated include: acetal, alcohol, alkene, alkyne, Ar-X, cyano and ethers. Furthermore the stereochemical integrity of the coupling partners is retained in two representative examples with an epimerisable carbon centre. This procedure enables the coupling of less nucleophillic amines such as anilines. However, the reaction yields are diminished when highly electron poor anilines are used, or when highly sterically hindered esters or amines are used.
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Bandi, Venu Gopal. "Synthesis and Photochemical Studies of Wide-Band Capturing Sensitizers Capable of Light Energy Harvesting." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862881/.
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Artificial photosynthesis, for the purpose of converting solar energy into fuel, is one of the most viable and promising alternative approaches to solve the current global energy and environmental issues. Among the challenges faced in artificial photosynthesis is in building photosystems that can effectively and efficiently perform light absorption and charge separation in broad-band capturing donor-acceptor systems. While having a broad-band capturing antenna system that can harness incoming photons is crucial, another equally important task is to successfully couple the antenna system, while maintaining its optical properties, to an energy or electron acceptor which serves as the reaction center for the generation of charged species of useful potential energy. The stored potential energy will be utilized in different applications such as driving electrons in solar cells or in splitting water for the generation of fuel. Hence, the particular endeavor of this thesis is to study and synthesize molecular/supramolecular systems with wide-band capturing capabilities to generate long-lived charge separated states. The sensitizer used in building these systems in the present study is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, for short, BF2 chelated Azaboron dipyrromenthene or AzaBODIPY. A handful of novel donor-acceptor systems based on AzaBODIPY have been successfully designed, synthesized and their photochemistry have been investigated using various techniques. In these systems, Azabodipy has been covalently attached to several donors like porphyrin, bodipy, subphthalocyanine, phenothiazine, ferrocene, bithiophene and effectively coupled to an electron acceptor, C60. These systems have been fully characterized by NMR, Mass, optical absorption and emission, X-ray crystallographic, computational, electrochemical, and photochemical studies. It has been possible to demonstrate occurrence of efficient electron and energy transfer events and long-lived charge separated states upon photoexcitation in these model compounds. By changing the arrangements of the donor and acceptor entities, it has also been possible to show directional, through-space and through-bond electron transfer processes. The present study brings out the importance of utilizing near-IR sensitizers in building solar energy harvesting model systems.
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Stratton, B. "Aspects of structure-reactivity correlations." Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382852.
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White, Brittany. "The Synthesis of Functionalized Cycloparaphenylenes as Novel Biocompatible Fluorescent Probes and Organic Materials." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24521.
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Conjugated macrocycles have emerged as novel structural motifs that modulate the electronic properties of organic molecules because of their strained and contorted structures. Cycloparaphenylenes, known as nanohoops, are a particularly attractive scaffold for the design of new types of carbon nanomaterials because of their size-selective synthesis, radially oriented π-systems and tunable electronic properties. The development of modular syntheses of nanohoops over the past decade should enable the preparation of substituted derivatives that can be tuned for applications in biology and materials science.
Chapter I provides a brief overview of conjugated macrocycles recently reported in the literature with a discussion of the structural effects that are responsible for the remarkable properties of this class of molecules. Chapter II highlights a scalable and mild synthetic approach developed in our lab to prepare nanohoop conjugated macrocycles and expands the generality of this methodology with the formal synthesis of natural product Acerogenin E. Chapter III describes the synthesis of cycloparaphenylenes with versatile functional handles and uncovers the reactivity of the strain nanohoop backbone under reaction conditions that promote the formation of radical cations. Chapter IV takes advantage of the functional groups described in chapter III to develop the first example of nanohoops as a new class of biocompatible fluorophores. Chapter V details a novel synthetic approach that enables the incorporation of the linear acene pentacene into the nanohoop backbone and reports our findings on the impact that the macrocyclic structure has on the properties of this organic semiconductor. In summary, the findings discussed in this dissertation provide synthetic strategies for the selective functionalization of nanohoops and highlight this class of molecules as a novel scaffold for the design of new types of carbon nanomaterials.
This dissertation includes previously published and unpublished co-authored material.
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Cuccia, Louis A. "Biophysical properties of dimeric phospholipids." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=42007.
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A series of unusual bipolar and bis-phospholipids (dimeric phospholipids) have been studied. The structure, conformation, morphology and biophysical properties of the resulting phospholipid aggregates were investigated.Deuterium magnetic resonance spectroscopy ($ sp2$H NMR) was used to study and characterize the conformation and acyl chain order in oriented bipolar lipid membranes. The $ sp2$H-NMR studies indicated a large and constant value for the order parameter (S$ rm sb{mol})$ for all positions along the bipolar lipid diacyl chain for mechanically oriented, magnetically oriented and unoriented samples. This indicates that the great majority ($>$90%) of the bipolar lipid exists in a highly ordered spanning conformation.
Dimeric phospholipid aggregate morphologies were studied using $ sp{31}$P NMR, small angle X-ray scattering, electron microscopy, differential scanning calorimetry, and the Langmuir film balance technique in order to study the relationship between lipid structure and aggregate morphology. Dimeric phospholipids favour a lamellar morphology. A number of lipid structure-dependent features have been observed including tri-lamellar structures, extended ripple phases and hexagonal phases.
Dimeric and non-hydrolyzable phospholipids were used to study the phenomenon of interfacial activation of extracellular phospholipase A$ sb2$ (EC. 3.1.1.4) (PLA$ sb2)$ in relation to lipid phase, substrate conformation and mobility. Kinetic results and product analyses are consistent with a situation where the spanning conformer of bipolar phospholipids is resistant to PLA$ sb2$-catalyzed hydrolysis but the hairpin conformer is readily hydrolyzed. Finally, an analysis of interfacial kinetics in non-hydrolyzable matrices indicated varying degrees of interfacial inhibition and hydrolysis product activation. This has not been explicitly recognized before and affects the choice of assay conditions for PLA$ sb2.$
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Jin, Jing. "The application of niobium compounds as catalysts in continuous flow reaction." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50484/.
Full textAbstract:
This Thesis describes the application of niobium oxide and niobium phosphate as solid acids for conducting continuous flow reactions, such as the Friedel-Crafts Reaction and the Skraup Reaction, and also as supports for photosensitiser immobilisation. Chapter 1 introduces the concepts of green and sustainable chemistry, and give a review of niobium and niobium compounds, especially niobium oxide and niobium phosphate as well as their applications. A summary of flow chemistry is also presented. The continuous flow systems used to conduct the work of this Thesis are described in Chapter 2. Chapter 3 introduces continuous alkylation of aniline with dimethyl carbonate or methanol over niobium solid acids. The synthesis process is automated by a self-optimisation system to search the best conditions for different products, including the NH2 group methylation product monomethyl aniline and dimethyl aniline, and the Friedel-Crafts alkylation product N,N-dimethyl-p-toluidine. Chapter 4 describes the first exploration of the continuous Skraup synthesis of quinolones with heterogeneous catalyst niobium phosphate. A dissymmetrics substituted quinoline compound, 4-(quinolin-6-yl methyl)aniline, was synthesized, and its crystal was grown and the structure was determined by crystallographic analysis for the first time. Chapter 5 discussed the immobilisation of a photosensitiser meso-tetraphenylporphyrin on niobium solid acids, and the activity of these supported photocatalysts in continuous photo-oxidation, including the photo-oxidation of α-terpinene to ascaridole and the semi-synthesis of an antimalarial drug, artemisinin ART. Finally, Chapter 6 summarises the work described in this Thesis and examines the success of the techniques and approaches discussed. A summary of potential routes for further study is also presented.
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Jalali, Elnaz. "Regiospecific P-Bromination of Activated Aromatic Systems – Greener Approach." TopSCHOLAR®, 2017. http://digitalcommons.wku.edu/theses/1950.
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The halogenated derivatives of heterocyclic compounds (haloarenes) are highly utilized in many fields of chemistry, including drug discovery, medicinal, and material chemistry. There are a variety of ways to functionalize an aromatic system and introduce halogen substituent into the ring. However, electrophilic aromatic substitution (EAS) has been the focus of growing attention, particularly for electronrich substrates.
Electrophilic aromatic bromination protocols are one of the most important electrophilic aromatic substitution reactions. However, preparation of bromoarenes classically recommends the use of highly oxidative agents along with utilizing various metal catalysts in a halogenated solvent. The corrosive and toxic nature of these reagents and need of harsh conditions for these protocols make their utility less desirable in current practice. Furthermore, lack of regioselectivity for most substituted aromatics is the other distinguished drawback, since most products contain ortho/para directors which afford a mixture of isomers.
The innovation of our procedure for the bromination of various substituted aromatic compounds is twofold in that highly regiospecific para-bromination of activated aryls by treatment with NBS has been accomplished. Although various reaction mediums, such as cyclohexane, acetone, and acetonitrile has been used in this procedure, the significant high yields of the product formation along with the very short reaction times using acetonitrile make this approach more attractive. That this regiospecific p-substitution takes place under such mild conditions leads us to question whether it is EAS.
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Walpita, Janitha Kumara. "Iminium Based Electrocaralysts for Water Oxidation and Organic Photohydrides for Proton Reduction." Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1431967855.
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Liska, Tadeas. "Bis(imidazolyl)carbazolide Platinum(II) Alkynyls: Synthesis, Characterization, and Photophysical Properties." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1626960987919156.
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Tessema, Tsemre. "PREPARATION AND EVALUATION TECHNIQUES OF POROUS MATERIALS AND MIXED MATRIX MEMBRANES FOR TARGETED CO2 SEPARATION APPLICATIONS." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/5044.
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The use of porous sorbents for physisorptive capture of CO2 from gas mixtures has been deemed attractive due to the low energy penalty associated with recycling of such materials. Porous organic polymers (POPs) have emerged as promising candidates with potential in the treatment of pre- and post- fuel combustion processes to separate CO2 from gas mixtures. Concurrently, significant advances have been made in establishing calculation methods that evaluate the practicality of porous sorbents for targeted gas separation applications. However, these methods rely on single gas adsorption isotherms without accounting for the dynamic gas mixtures encountered in real-life applications. To this end, the design and application of a dynamic gas mixture breakthrough apparatus to assess the CO2 separation performance of a new class of heteroatom (N and O) doped porous carbons derived from a Pyrazole precursor from flue gas mixtures is presented.
Here in, two new benzimidazole linked polymers (BILPs) have been designed and synthesized. These polymers display high surface while their imidazole functionality and microporous nature resulted in high CO2 uptakes and isosteric heat of adsorption (Qst). BILP-30 displayed very good selectivity for CO2 in flue gas while BILP-31 was superior in CO2 separation from landfill gas mixtures at 298 K and 1 bar. Additionally, a new POP incorporating a highly conjugated pyrene core into a polymer framework linked by azo-bonds is presented. Azo-Py displays a nanofibrous morphology induced by the π-π stacking of the electron rich pyrene core. Due to its high surface area and microporous nature, Azo-Py displays impressive CO2 uptakes at 298 K and 1 bar. Evaluation of the S value for CO2 separation of Azo-Py revealed competitive values for flue gas and landfill gas at 298 K and 1 bar.
Finally, a highly cross-linked benzimidazole linked polymer, BILP-4, was successfully incorporated into Matrimid® polymer to form a series of new mixed matrix membranes. The surface functionality of BILP-4 was exploited to enhance the interaction with Matrimid® polymer matrix to produce robust MMMs which displayed significantly improved CO2 gas permeabilities and ideal selectivities for CO2/N2.
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Gumus, Selahaddin. "Secondary Electronic and Solvent Effects on Regiospecific P-Bromination of Aromatic Systems." TopSCHOLAR®, 2018. https://digitalcommons.wku.edu/theses/3031.
Full textAbstract:
Bromoarenes are important aromatic building blocks that are commonly used to synthesize various functional compounds in pharmaceutical, agrochemical and related industries.1,2 This great demand for bromoarenes makes their preparation a widely studied area of synthetic organic chemistry. However, further understanding of the reactivity and regiochemistry of aromatic functionalization reactions is still necessary, as much about the secondary substitution and solvent effects remain unknown.
Resonance Theory is a widely used theoretical model to predict the regiospecifity and reactivity of the bromination of various aromatic compounds.3 The reactivity and regiospecificity of many substituted aromatic compounds is well explained using resonance theory.4 However, kinetic understanding of the p-bromination of halosubstituted aromatic compounds has not been investigated to the best of our knowledge.5,6In this thesis, the reactivity and regiospecifity of the p-bromination of activated secondary substituted aromatic compounds as well as media effects on the process will be discussed.
Synthesizing bromoarenes has been accomplished using many different experimental setups.7-11 N-bromosuccinimide is the most highly utilized electrophilic aromatic brominating agent. Many of the NBS- based aromatic bromination reactions have been reported using strong acids, strong bases, halogenated solvents, nonpolar solvents and polar solvents alike.12 The bromination reactions reported herein were performed using two different solvents, acetonitrile and acetone, to investigate the effects of solvent polarity on p-bromination. Although acetonitrile is one of the most commonly used solvents in the p-bromination of aromatic compounds, acetone has not been investigated.
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Moody, Leslie Shane. "Towards the Design and Syntheses of Novel Triads Comprising Single Robson-Type Macrocyclic Dicopper(II) Cores Flanked by Two Terminal Polypyridyl Ruthenium(II) Complexes." Digital Commons @ East Tennessee State University, 2008. https://dc.etsu.edu/etd/2010.
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Progress toward the syntheses of new tetranuclear bimetallic complexes of copper(II) and ruthenium(II) was realized. The designed triads comprise a central binuclear copper(II) complex with a tetraiminodiphenolate macrocyclic Robson-type compartmental ligand. In the envisioned complexes, the macrocyclic core is further functionalized by attachment of two polypyridyl ruthenium(II) complexes. A novel dibrominated dicopper(II) Robson complex was formed by the 2:2:2 condensation reaction of 4-bromo-2,6-diformylphenol and 1,3- diaminopropane with cupric chloride. Similarly, a new dibrominated dizinc(II) was synthesized from zinc tetrafluoroborate and the same diamine and dialdehyde. The new dicopper(II) complex did not heterocouple with borylated substrates under explored Suzuki reaction conditions. 5-Bromo-2-(methoxymethoxy)benzene-1,3-dicarboxaldehyde successfully heterocoupled with 4-tert-butylphenylboronic acid under Suzuki conditions. 4'-(4-Neopentylglycolatoboronphenyl)-2,2':6',2-terpyridine also coupled with 5-bromo-2-(methoxymethoxy)benzene-1,3-dicarboxaldehyde to give, after deprotection, 2,6-diformyl-4-(4-[2,2':6',2"-terpyridin]-4'-ylphenyl)phenol. This new dialdehyde, a precursor to the title complexes, was treated with (4'-(4-methylphenyl)-2,2':6',2"-terpyridine)RuCl3 under reducing conditions; however, the desired [(4'-(4-methylphenyl)-2,2':6',2"-terpyridine)Ru(4'-(3,5-diformyl-4-hydroxyphenyl)-2,2':6',2"-terpyridine)]2+ was neither isolated from nor detected in the reaction mixture.
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Bawazeer, Wafa Abubaker S. "Tandem reactions for sp3-rich scaffold synthesis." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/32195/.
Full textAbstract:
Several novel methodologies were explored with the general purpose of rapid access to molecular complexity and sp3-rich scaffolds. A number of novel scaffolds were successfully synthesised, utilising two-directional synthesis and tandem reactions. The chemistries applied have been demonstrated to be capable of readily fabricating many novel and interesting diverse molecular scaffolds. Indeed, the azaspirocyclic cores found in halichlorine and pinnaic acid were synthesised using this approach starting with ethyl formate. More diverse scaffolds were generated from simple symmetrical linear molecules derived from ethyl formate, utilising the nitrone produced in situ by the treatment of the central ketone with either hydroxylamine hydrochloride or amino acids. These afforded number novel skeletons [A-C], which are expected to have interesting biological activity. In addition, they are conceivably useful skeletons in the synthesis of natural products, or in drug synthesis due to its high saturation (high Fsp3) characters. Using the tandem reactions, we have also managed to develop a rapid synthetic route to an sp3 -rich chemical scaffold [F] derived from novel isoxazolidine scaffold [E]. This project has been published with a contribution of other group member. We were interested to synthesise of some natural products. We tried to explore the possibility of developing an enantioselective synthesis approach to the key intermediate in the synthesis of hippodamine [H], few attempts toward the synthesis of the marine alkaloids phakellin [I]. Several novel applications of chiral sulfinimines were explored. Initially some preliminary results toward the synthesis of piperidine dione [I] were recorded. Successful attempts of tert-butyl sulfinimines with dianion tert-butyl-acetoacetate afforded a range of cyclic compound piperdine dione [J] in a good yield.
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Feast, George C. "Aziridinations of tethered allenes." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:9b7b1fa7-c2fd-4cf1-94f8-333504332d7d.
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This thesis describes the synthesis and reactivity of previously unprecedented bicyclic methylene aziridines via rhodium(II) catalysed cyclisation of α-allenic N-tosyloxycarbamates. These aziridines undergo reaction with organocuprates to give cis- disubstituted oxazolidinones by nucleophillic attack at the vinylic centre; plausible mechanisms for this process are discussed. Similar rhodium(II) catalysed cyclisations of β-allenic sulfamates afford cyclic enamines, aminocyclopropanes or bicyclic methylene aziridines; the product ratio depends on the allene substitution pattern. Suitably-designed substrates undergo trapping of the proposed intermediate amino allyl cation by internal nucleophiles or by cycloaddition. Finally, thermally-induced intramolecular cycloadditions of γ-allenic azides are described that give triazolines or [1,2,3]-triazoles.
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Akdeniz, Ali. "Sensing of Enantiomeric Excess in Chiral Carboxylates." Bowling Green State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1465223828.
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Pandey, Kadel Usha. "Metal-free electrocatalysts for oxygen evolution reaction and photocatalysts for carbon dioxide reduction reaction." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1513279535028305.
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Pitre, Spencer Paul. "Visible-Light Mediate Redox Processes: Strategies and Applications in Organic Synthesis." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36453.
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Over the past decade, the field of photoredox catalysis has garnered increasing amounts of attention in the organic chemistry community due to its wide applicability in sustainable free radical-mediated processes. Several examples have demonstrated that under carefully optimized conditions, efficient and highly selective processes can be developed through excitation of a photosensitizer using inexpensive, readily available light sources. Furthermore, these reactions can generally be performed under milder conditions than thermal reactions, as all the energy required to overcome the reaction barrier is supplied by light.
Despite all these recent advancements in the field, many of these discoveries often lack in depth investigations into the excited state kinetics and underlying mechanisms. Furthermore, the vast majority of these transformations are photocatalyzed by ruthenium and iridium polypyridyl complexes. Not only are these precious metal catalysts extremely costly, but these metals are also known to be toxic, limiting their potential use in the development of pharmaceutical protocols. Herein, we present our solutions to these shortcomings, which involve a three-prong approach in the development of novel protocols, understanding the underlying mechanisms through detailed kinetic analysis, and by the development of new tools to facilitate mechanistic investigation for practitioners who may not possess specialized photochemical equipment.
In this work, we were the first to demonstrate that radicals derived from amines, commonly employed as “sacrificial” electron-donors, can also act as reducing agents in photoredox transformations. We also present examples in which Methylene Blue, an inexpensive, non-toxic organic dye, can be employed as a viable alternative to ruthenium complexes for photoredox transformations. By employing a photosensitizer with more favourable excited state kinetics for electron-transfer, we successfully demonstrated that Methylene Blue could be used to increase the efficiency of a previously developed photoredox transformation.
While employing organic dyes is an excellent strategy to lowering the cost of photoredox transformations, another viable strategy is to employ heterogeneous semiconductors. Titanium dioxide is an example of a semiconductor which is often employed in photocatalytic applications due to its low cost, desirable redox properties, and high chemical stability which allows for continued use. However, titanium dioxide has seen limited use in organic synthesis due to the requirement of UV irradiation for excitation. Herein, we present a process which led to the discovery of visible light photochemistry with titanium dioxide, generated through the adsorption of indole substrates creating a new, visible light absorbing complex. Employing this strategy, we were able to promote the photocatalytic Diels–Alder reaction of indoles with electron-rich dienes, giving access to valuable tetrahydrocarbazole scaffolds.
Finally, in order to facilitate the characterization of chain processes in photoredox catalysis, we have successfully developed a visible light actinometer based on the ubiquitous photocatalyst, Ru(bpy)3Cl2. This actinometer offers many advantages compared to other visible light actinometers, such as completely eliminating the need for spectral matching, as the actinometer is also the photocatalyst. This technique should provide researchers with a mechanistic tool to properly characterize chain propagation in the transformation of interest.
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Parvez, Arshad. "Alkali Extraction Test as a Predictor for Self-Heating in Coal." TopSCHOLAR®, 1986. http://digitalcommons.wku.edu/theses/1817.
Full textAbstract:
The self-heating of coal is a serious problem that has always affected the coal industry. Self-heating has been studied around the world for more than 100 years by many investigators, yet no accurate method of predicting self-heating in coal has been developed.
The objective of this research was to investigate the factors contributing to the self-heating in coal and to develop methods to predict the self-heating in coal and to develop methods to predict the self-heating susceptibility of various coals. A data bank containing analytical data, transportation histories, and results from laboratory tests was established at Western Kentucky University. A laboratory test that gave very encouraging results is an extraction test using sodium hydroxide solutions. Absorbances of the extract solutions from 15 coal samples obtained from barges of coal shipped from the Illinois Basin coal fields to the New Orleans area compared very well with the incidences of self-heating in the 15 barges. The fact that these coals were shipped in the summer when conditions are more favorable for self-heating to take place may have led to the strong correlation of the alkali extract solution absorbances and the final temperatures of the coal in the barges. Tests with coal samples obtained from barges shipped in the other seasons of the year did not yield very good correlations. The poor correlation between self-heating and the alkali extraction test absorbances was due to the lack of accurate temperature data, since the temperature of the coal at the time of loading was not available. The correlation of the absorbances of the extract solutions with parameters such as Btu/lb, oxygen, sulfate sulfur, and free-swelling index was very good.